The vertebrae of the human spine are arranged in a column with one vertebra on top of the next. Between each vertebra exists an intervertebral disc that transmits force between adjacent vertebrae and provides a cushion between the adjacent vertebrae.
Sometimes, back pain is caused by degeneration or other deformity of the intervertebral disk (“diseased disk”). Conventionally, surgeons treat diseased discs by surgically removing the diseased disc and inserting an implant in the space vacated by the diseased disk, which implant may be bone or other biocompatible implants. The adjacent vertebrae are then immobilized relative to one another. Eventually, the vertebrae grow into one solid piece of bone.
Currently, it is difficult to insert the bone graft into the vacated space and fuse the adjacent vertebrae. The current process of inserting a bone graft and fusing the adjacent vertebrae will be explained with referring to FIGS. 1 and 2. FIG. 1 shows two adjacent vertebrae 102 and 104. Located between vertebrae 102 and 104 is an intervertebral space 106 partially filled by an implant 108. When the implant 108 is first inserted into the intervertebral space 106, the adjacent vertebrae 102 and 104 are manually kept apart by the surgeon using, for example, a retracting device (not shown). As shown in FIG. 2, once the implant 108 is placed, the surgeon releases the adjacent vertebrae 102 and 104 allowing them to squeeze the implant 108 and hold the implant 108 in place.
To immobilize the vertebrae 102 and 104 with the implant 108 in place, the surgeon next applies a cervical plate 202 over the adjacent vertebrae 102 and 104. Cervical plate 202 may have a central viewing window 204 and one or more screw holes 206, in this example four screw holes 206a–206d are shown. Four bone screws (which will be identified by reference numerals 208a–208d) would be screwed into the vertebrae using the screw holes 206 to anchor the cervical plate to the vertebrae and immobilize the vertebrae with respect to one another.
The bone screws 208a–208d absent a locking mechanism tend to reverse thread, which is also known as backing out. Locking mechanisms have been developed to inhibit the bone screws from backing out. Some of the devices included caps or plates that extend over the screw holes 206 to inhibit upwards movement of bone screws 208a–208d. Other devices include a frictional engagement between a bushing and the bone screws 208a–208d. 
Although many devices exist that satisfactorily inhibit backout of the bone screws, it would be desirous to develop a device to inhibit the bone screws from backing out.